Apologies! Darktide is DX12 only - my brain defaulted to a Vermintide support suggestion 
M’bad.
Please try running through the performance solutions linked above.
It may also be helpful to check and disable any background applications that are running via Task Manager to see if anything is interfering, or to try a Selective Startup:
- Press the Windows key
- Type ‘msconfig’ and select ‘System Configuration’
- On the ‘General’ tab, select ‘Selective Startup’
- Deselect ‘Load startup Items’
- Reboot your PC
If the issue no longer occurs after having performed the Selective Startup, try re-introducing your programs one-by-one to determine which is the culprit.